Morris was the apprentice of Charles Willing from approximately 1750 - 1754. During this time, he also befriended Willing's son, Thomas Willing. When Charles Willing passed away in 1754, his successful shipping-banking firm was inherited by Thomas Willing, who invited Morris to join the company as a partner. Morris agreed, and the two men founded the Willing, Morris & Co. firm, which quickly grew into a lucrative and respected business.

George Washington personally wrote to Morris in 1786, expressing hopes that he find support in ending the process of slave trading in a democratic way. Morris, at the time, had profited largely on financing slave trading. Washington referenced, in his letter, the fact that escaped slaves made their way north for safety, which is the first known acknowledgement of the Underground Railroad in writing. Morris met Washington in 1781, at the latest, when helping Washington and his troops navigate the land. Morris and Washington became friends, and Morris was one of the most powerful backers of Washington when he was being elected President. Upon Washington's election, he asked Morris to accept the position of Secretary of the Treasury in 1789, but Morris declined and instead suggested Alexander Hamilton.

While representing Pennsylvania on the Second Continental Congress from 1775 - 1778, I worked closely with John Adams.

Morris was a colleague of John Barry, the naval officer, and of John Dickinson.

Thomas Paine and Henry Laurens were opposers of Morris, and accused him of war profiteering in 1779.

Morris was a colleague and business partner in land speculation with James Greenleaf.

Arthur Lee was a lifelong and bitter enemy of Morris. Lee spread rumors about Morris' alleged involvement in a conspiracy.

Alexander Hamilton was a friend and close colleague of Morris'. They shared the same political views and often backed each other's opinions. When Washington asked Morris to accept the position of Secretary of the Treasury in 1789, Morris declined, but suggested that Hamilton be chosen instead.

In 1794, Charles Pierre L'Enfant began designing and building a vast mansion for Morris in Philadelphia. The project was never completed, however. In later years, the marble used to start the unfinished house was sold off and ended up on monuments in Rhode Island and Charleston.